Add TetheringPrivilegedTests to postsubmit

Also ignore DadProxyTest before S because it is only enabled from S.

To using ignore test rule, replace AndroidJunit with DevSdkIgnoreRunner.
It is fine because the we don't use the test UI (e.g. running test in UI
thread).

Test: atest TetheringPrivilegedTests
Change-Id: I701ee877520f78ded2394adbae1f4d9dd612d700
3 files changed